I will tell you how I make my espresso and you tell me what is my mistakes
1- mix all kind of bean in my blend in plastic box
I use for 10 kg of espresso 5kg colombian sobramo
3 custa rica 2 Brazilian santos
2- I put them together in my roster machine when the temperature is 180
After I got my medium color I Take it out of the machine this takes 90 mint
3- I keep it out of the machine to be a little cold
4 - I take roasted bean from machine using the small plastic box and put it in big plastic box for 12 hours
After that I pack it in my Almnum bags to sale it

Re 1: Your beans should roast fairly well blended. For your future consideration, you should only mix similar beans together to roast them. So, what to put together and keep apart. Size is one factor; so keep any peaberries apart. Density is another; so roast hard and soft beans separately.
Re 2-1: 180 C is a little low. something around 200 to 210 would be better. You need to build up the heat so that the beans have a chance to roast evenly during development. The higher temperature will help to drive off the moisture.
Re 2-2: Roasting by colour is but one of the many ways to run a roaster. Also, you should not only look when you think the roast is done. For example, when the roast hits about BT 150 C {Dry] the beans should change to yellow or very light tan colour. If this does not happen at that temperature and nothing else is wrong, it's an indication that there is something wrong with your probe placement or calibration. If you're not using a temperature probe, then you should use the trier to watch for this and note the time. I usually shoot for around 3 to 4 minutes to get there. If your beans take a long time to get to "Dry", then likely your roaster is not turned up hot enough when you charge (as above) or your roaster is overloaded.
Re 2-3: I'm not sure what "medium colour" would be. However, at the development stage you should also be going by sound. Generally, the sounds of first crack should be over for most roasts (except very light ones). Since you're shooting for a medium roast, the sounds of second crack should not have started. Overall, though, as others have mentioned, 90 minutes is way too long. A typical roast for me takes somewhere in the vicinity of eight or nine minutes, even 15 minutes is long for me and I'm roasting most beans to FC+ (i.e., moderately dark). Twenty minutes would be considered long enough for big drum roasters.
Re 3: Cooling should be done with a fan under a screened container, not just dropping and letting them sit (perhaps this is what you mean?). If you let them sit to cool, they will continue to roast (this is called "coasting").
Re 4: Letting them sit is a good idea before using, but not necessary if properly packed for sale. Aluminium bags, or any other impervious bag, should have a so-called 1-way valve on it to let the gasses escape. At the very least, unless packing in nitrogen-purged bags, there should be a little pin hole, otherwise the bags will gradually expand. We used to see this in the stores before N-purged packaging became popular...every so often a bag would be so expanded it looked like it might explode!

That's all I can think of suggesting. You probably already know all or most of this. I'm just an amateur roaster...I don't roast for sale.